Self-inking stamp



FIG. 1 is a perspective view of a self-inking stamp showing my new design;

FIG. 2 is a front view thereof;

FIG. 3 is a right side view thereof;

FIG. 4 is a top plan view thereof;

FIG. 5 is a rear view thereof; and,

FIG. 6 is a left side view thereof. 

The ornamental design for a self-inking stamp, as shown and described. 